Voltmeter



Oct. 9, 1928. 1,686,689

c; LE G. FORTESCUE VOLTMETER Filed y 15, 1924 WITNESSES: INVENTOR Charles LeG. Forfescue.

Patented Oct. 9, 1928.

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CHAIEtLTEiS LE G. FORTESCUE, CF PITTSBURGH, PENNSYLVANIA, ASSIGNOR TO WEST- I INGEGUSE ELECTRIC & MANUFACTURING COMPANY, CORPORATION OF PENN".-

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Application lfiled May 15,

tween two conductors is raised, a VlSlbl8'- corona discharge is produced at the surface of one conductor when the voltage gradient at the surface of this conductor is sufficiently great. For a given air pressure and temperature, the critical value of the voltage gradientis definitely fixed within narrow limits so that the discharge may be utilized in a voltage-measuring instrument.

In order to obtain an instrument which would cover a range of voltages,that is, form a corona discharge for any one of the several voltages,-it has been proposed to enclose the conductor in a suitable container and vary the temperature or pressure of the surrounding medium. This is a rather troublesome method and requires complicated apparatus.

Since the corona discharge is a function of the voltage gradient, it has also been proposed to construct an instrument covering a range of voltages by employing conductors of different sizes or a tapered conductor, as disclosed in U. S. Patent No. 1,289,068, issued December 31, 1918, to C. T. Allcutt and assigned to the Westinghouse Electric & Mfg. Company. The first mentioned arrangement was found undesirable because of the necessity for substituting different conductors and because the employment of conductors of difierent sizes permitted voltage readings only in steps. The latter device described in the Allcutt patent is rather complicated as it requires a shield for thetapered conductor.

Itis the objectof my invention to provide a simpler but equally effective corona voltmeter that will'read directly over a range of voltages by corona discharge. I obtain this result by employing two relatively movable conductors so arranged that varying the relationship of the conductors varies the voltage gradient upon the corona-forming conductor and thereby changes the required applied VOL'IVQMETER.

1924. Serial No. 713,439.

voltage for producing the corona discharge.

conductor and the corresponding applied voltage required to initiatecorona discharge. The formation of corona isindicated by an ammeter connectedin series with the corona voltmeter, a sharp deflection of the ammeter being obtained upon the formation of the corona discharge.

The detailed construction and the mode of operation of my. invention will be apparent from the accompanying drawings wherein Figure l is a plan View of one modification thereof, and Y i Fig. 2 is a side View of the same instrument.

lrepresents a conductor, the potential of which it is desiredto determine. Surrounding theconductor 1 is a hollow cylindrical conductor 2, having insulated flared ends 3 to produce a uniform electrostatic field. The conductor 2 is pivotally mounted upon an eccentric axis 4: and is provided With a pointer 5. As the conductor 2 is turned about the axis/l, the pointer 5 indicates its angular position uponthe scale 6. A current-measuring instrument 7 which may be of the DArsonval type, is connected to the conductor 2.

The operation of the device is as follows:

In order to measure the potential of the conductor 1, the movable conductor 2 is turned about the axis 4:- from its initial position shown until a. sharp deflection of the ammeter 7 indicates that corona discharge has been formed between conductors 1 and 2. At this .point,'the pointer 5 indicates the potential of the conductor 1, the scale 6 being preferably calibrated .to read voltages directly. e

is rotated about the axis 4, apart of the sur face of conductor 2 is brought nearer-to. the conductor 1, thereby increasing the voltage gradient at the surfaceof the latter. This voltage gradient is increased by the movement of the conductor 2 until corona forms upon the conductor 1. As we have'seen, for a given pressure and temperature, the forma tion of corona depends solely upon the voltage gradient. Therefore, the angular position of the conductor 2, as indicated by the pointer 5, provides a direct indication of the potential of conductor 1.

i I claim:

1. A voltmeter operable by means of corona discharge comprising normally concentric conductors having opposed cylindrical surfaces, one of said conductors being movable about an eccentric axis.

2. In combination, two normally concentric conductors one of which is rotativcly supported upon an eccentric axis, and a coronadischarge-indicating device connected to one of said conductors.

3: In combination, a stationary conductor, a movable conductor encircling said stationary conductor, means for changing the distance between the movable and the stationary conductors, means for indicating an electrical phenomena between said conductors, and means associated with said movable conductor for indicating the voltage producing said phenomena.

4. An electrostatic voltage-measuring systemcomprising a stationary elongated conductor, a hollow cylindrical conducting body encircling said conductor, said body being movable about an eccentric axis with respect to said conductor. whereby the distancebetween the body and the conductor may be changed, means for indicating the formation of corona between said body and said conductor, and a scale. associated with said movable body'for indicating'the magnitude of the voltage producing said corona;

5. An electrostatic voltmeter comprising CHARLES LE G, FORTESGUE. 

